The present invention relates to method for the regenerative treatment of mainly clay-bound foundry old sand for the re-use of the latter.
In the case of molding material circulation in a foundry, in which clay-bound greensand is used for the production of molds, old sand which occurs at the point of shaking-out is fed to a processing plant. This old sand is a mixture of mainly clay-bound molding sand and smaller parts of chemically bound core sand. Active bentonite and coked, porous, unused black substances (coal dust) are contained in the old sand. As a result of the action of heat of the casting metal, a portion of the bonding clay or bentonite is dead-burned, whereby a ceramic, adherent, porous surface layer or shell (burned fireclay) is formed on the quartz grains. This old sand can regain binding strength with addition of new bonding clay and water.
The molding material reprocessing systems operate with a high degree of efficiency. The result of this is that the quartz sand part, supplied by means of core sands, generates a surplus in the way of molding material which must be removed from the system. The transportation away and the dumping of this quantity of old sand entail costs and burden the environment.
The object of the present invention is to propose a method with the aid of which both economical regenerative treatment of foundry old sand, which treatment is easy to operate, and the recovery of usable dust become possible.